Heater



FIG. 1 is a front elevational view of a heater;

FIG. 2 is a rear elevational view thereof;

FIG. 3 is a right side elevational view thereof (the left side is a mirror image); and,

FIG. 4 is a top plan view thereof.

Thr broken lines are for illustrative purposes only and form no part of the claimed design. 

I claim the ornamental design for a heater, as shown and described. 